Electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), henceforth referred to as EVs, offer the promise of decreasing reliance on oil for transportation products and services. Commercial EVs are beginning to appear in the marketplace. One shortcoming that has been recognized is that charging of EV batteries takes a long time, limiting their daily utility. Another shortcoming in commercially available EVs is the low amount of energy delivered during a rapid charge due to their small pack size or limited bulk charge envelope.
To achieve a driving range of 300 miles or more, roughly equivalent to the range afforded by internal combustion engines (ICEs) using petroleum-based fuel, energy storage of 260 amp hours at 350 volts (or 91 kW-hrs) would be typically required. With the currently available technology, such a battery cannot be rapid charged to over 80% SOC within twenty minutes.
As an example of the dimension of the challenge, charging a battery module with 4 cells in series, each with a capacity of 260 amp hours, to 89% SOC in 20 minutes during an initial “bulk charge” phase requires an input current of 700 amps (260 amp hours*0.89 SOC*60 minutes/hour/20 minutes/0.9917 amp-hr efficiency=700 A). This level of charge current and bulk charge envelope are required to provide an EV with a driving range of up to 300 miles.
A battery module solution capable of repeated high-current rapid charging cycles with a large bulk charge envelope offers the promise of enabling motorists to experience the driving range afforded by internal combustion engines (ICEs) and may hasten the adoption of EVs.
A major barrier to high-current rapid charging is that batteries based on common chemistries, including lithium-ion, experience catastrophic failures when they are overheated. One cause of battery heating when rapid charging is the increased rate of the chemical conversion processes within the battery cell. A second cause of battery heating when rapid charging is the internal resistance of interconnects to each battery cell terminal. A third cause of battery heating when rapid charging is the ability to extract waste heat from the module. Lack of solutions to the aforementioned problems has thus far hindered commercial availabilty of rapid charge battery packs and high power charging systems.
Overheating of battery modules may prevent multiple rapid charge cycles during a day. This is because the waste heat generated during a twenty minute rapid charge and subsequent driving may cause a battery to reach temperatures that prohibit a second rapid charge in the absence of a prolonged cool down period after driving. Therefore, it would be desirable to have a battery module capable of high-current rapid charging that applies thermal management treatments to avoid overheating.
Prior art air cooling systems for battery packs draw air in at the front of a battery pack and exhaust heated air at the rear. Air heats up as it travels through the pack. So the air's cooling capacity diminishes as it flows through the pack, resulting in battery cells at the rear of a pack that are hotter than those at the front. Therefore, it would be desirable to have an air cooled battery pack that draws air in and circulates fresh air at every module to maintain thermal uniformity among cells within each module, and among all the modules in a battery pack.
In summary, a battery module that rapidly charges at high current, to a high SOC, with high thermal uniformity across all cells in the module, and to do so repeatedly without exceeding upper termperature limits, thus maximizing an EV's daily driving range, would be highly desirable.